The natural environment is being overwhelmed by non-biodegradable, petroleum-based polymeric materials. The ever-increasing demand for such materials has increased dependence on petroleum products and left landfills overflowing with non-renewable, indestructible materials. The great current interest in cheap, biodegradable polymeric materials has recently encouraged the development of such materials from readily available, inexpensive natural sources, such as carbohydrates, starches and proteins, but relatively little work has been done on the conversion of fats and oils to such materials. The development of polymeric materials from biological oils, such as vegetable and fish oils, could dramatically expand and diversify the market for biological oils, while also improving the environment and reducing dependence on petroleum products.
Vegetable oils and fish oils are readily available in large quantities throughout the world. Of all biological oils, soybean oil is probably the most preferable oil for industrial use because it is inexpensive and produced in extremely large volume.
Soybean oil is principally composed of three unsaturated fatty acids: oleic acid, linoleic acid (also called linolic acid), and linolenic acid. These three fatty acids are the primary unsaturated fatty acids found in vegetable oils. Palmitoleic acid is primarily derived from fish oil. Arachidonic acid is primarily derived from animal sources. These five fatty acids comprise the major unsaturated fatty acids of commercial value. The structures of these fatty acids are shown below:
CH.sub.3 (CH.sub.2).sub.5 CH.dbd.CH(CH.sub.2).sub.7 CO.sub.2 H palmitoleic acid CH.sub.3 (CH.sub.2).sub.7 CH.dbd.CH(CH.sub.2).sub.7 CO.sub.2 H oleic acid CH.sub.3 (CH.sub.2).sub.4 CH.dbd.CHCH.sub.2 CH.dbd.CH(CH.sub.2).sub.7 CO.sub.2 H linoleic acid CH.sub.3 CH.sub.2 CH.dbd.CHCH.sub.2 CH.dbd.CHCH.sub.2 CH=CH(CH.sub.2).sub.7 CO.sub.2 H linolenic acid CH.sub.3 (CH.sub.2).sub.4 (CH.dbd.CHCH.sub.2).sub.4 (CH.sub.2).sub.2 CO.sub.2 H arachidonic acid
The fatty acids typically occur in nature as esters, the carboxylic hydrogen being replaced by, for example, a methyl group, ethylene glycol, or glycerol.
Fish oil is a by-product of the production of fish meal. Fish oil has a triglyceride structure with a high percentage of polyunsaturated .omega.-3 fatty acid side chains, which contain 5-7 non-conjugated c--c double bonds. Chemical analysis indicates that fish oil is a mixture of primarily three key structures:
docosa-4,7,10,13,16,19-hexaenoic acid (DHA, 24.72%); PA1 eicosa-5,8,11,14,17-pentaenoic acid (EPA, 31.68%) and PA1 docosa-7,10,13,16,19-pentacnoic acid (DPA, 4.27%).
This high degree of unsaturation has prompted researchers to examine fish oil as a potential monomer for polymerization or co-polymerization. The reports that have appeared in the literature typically refer to the production of viscous oils.
Very short oligomers such as dimers and trimers have been produced from soybean oil using thermal polymerization processes, as described by R. W. Johnson, et al., Polymerization of Fatty Acids, Fatty Acids in Industry 153-75 (1989). However, these processes are poorly controllable. In addition, the processes produce mainly dimers and trimers, and tend to destroy carbon-carbon double bonds.
What is needed is a process capable of polymerizing the unsaturated fatty acids in biological oils to produce useful plastic materials. Also needed is a process that can produce a high yield of product with a small catalyst load in a controlled process that minimizes the use of non-renewable, environmentally harmful materials.